Alright, picked up another project, 87 F150, 5.0 EFI, dual tanks, supposedly starts missing after 20 mins. All I can get it to do is shut down and then barely turn over. I jumped it and had to ground directly to the engine, then it spun over fine and cranked up. So to me a bad ground, I rigged up another cable but after 4 cranks it is barely turning over again. Timing is 10 degrees spout out. Batt measures 12.7, 14.5 at idle. Could it be a funky computer ground? Also, fuel is 37 psi at idle.
Also the tank switch won't switch and the gas gauge is pegged, I see a fuel junction on the frame at the pump, but no wires. Does this just have the external pump for both tanks?

 

Did a little reading, I unhooked the frame pump and grounded the test connector and don't hear either in tank pump, would it run off just the frame pump for awhile?

 

Only if there's fuel in the reservoir. Click my black Bronco in my sig & look thru the '84-89 Fuel Reservoirs album.

The EEC has nothing to do with cranking - remove, clean, & tighten every terminal on the 2 heavy battery cables, all the way down to the block & starter. Do 1 at a time so you don't mix anything up.

What do you mean the switch won't switch - it doesn't move? Buy a new one from a parts store (like Parts+Plus).

The gauge pegs full when the sender goes to open circuit. That usually happens due to wear, so if it shows open from the Y/Wh wire's terminal on the tank to the Bk wire's terminal, you'll have to pull the sending unit out. Some pickup owners say it's easier to lift the bed than to drop the tank.

 

Somehow it is running as long as you stay under 25mph????

The switch won't switch tanks, I see now where the pumps have to work to make the valve work. I have pulled the bed off and nieter pump seems to be working. I pulled the front pump and it won't run straight from a batt. What worries me now is that I grounded the gauge wire and it didn't drop. I see that the contacts in the sender were basically gone, so ordered 2 new pump assems, and will go from there.

 

The open circuit can also occur at the instrument cluster connectors. Pull it (be careful with the shift indicator tube) & polish the film circuit terminals with brown paper or a pink eraser.

 

Oh, I unplugged the selector switch and the gauge dropped. I'll swap in the pumps and then see what happens, hopefully it will all straighten out.
your diagrams and such have been a big hepl, thanks.

 

I Had alot of fuel pump relay problems with my 89 f150 5.0.......

 

That's odd... It should have pegged high. The level sender circuit(s) go thru the tank selector switch, so unplugging it also creates an open circuit.

 

Sorry forgot, I unplugged the switch and grounded the lead and the gauge dropped.
The pumps seemed to fix the running. When first installed both gauges showed on the full line, both tanks are full. Now both look to have pegged again. The switch is swithing the pumps though.

 

There's a totally separate set of contacts in the switch for the gauge. It can work for the pumps but not for the gauge, so test each set of terminals. If either fails, repair (not recommended) or replace the switch.